Liquids in various systems are plagued by unwanted microbial growth due, for example to one or more of environmental conditions, composition of the liquid, exposure to atmospheric oxygen and the like factors. In an effort to mitigate this unwanted microbial growth, one or more of various chemical microbiocides or biocides typically are added periodically to the system, e.g., whenever liquid levels are adjusted and/or on a set time schedule. The terms microbiocide and biocide are used interchangeably herein. Such microbiocides include, but are not limited to, chlorine-containing microbiocides, bromine-containing microbiocides, and the like and combinations thereof. Usually, the concentration of a microbiocide in a system, which can vary due to evaporation, chemical neutralization, deactivation, degradation and the like, is not known at any given time. Instead, a predefined amount of microbiocide, for example in combination with one or more additives in a predetermined ratio, is added to the system at regular maintenance intervals or whenever liquid levels reach a point at which liquid level adjustment is required or appropriate.
Various methods of introducing additives to fluid systems, generally, have been proposed. Rohde U.S. Pat. No. 3,749,247 describes a container for releasing an oxidation inhibitor into hydrocarbon-based lubricating oil in a working engine. The oxidation inhibitor is held in a polyolefin container that permits the additive to permeate through the container wall into the oil. A further approach is described by Lefebvre U.S. Pat. No. 5,591,330, which discloses a hydrocarbon oil filter wherein oxidation additives in a thermoplastic material are mounted in a casing between a particle filtering material and a felt pad. Reportedly, the thermoplastic material dissolves in the presence of high temperature oil thereby releasing the additives. Additionally, an additive release device for use in an engine hydrocarbon fuel line is proposed by Thunker et al U.S. Pat. No. 5,456,217. The latter device comprises a partially permeable cartridge positioned in the filling neck of the fuel tank so that whenever fuel is added a portion of the additive contents of the cartridge is released into the tank.
Aqueous-based coolants present an environment distinct from those of hydrocarbon fluids. For instance, most thermoplastics do not dissolve in aqueous solutions. Moreover, relatively large quantities of additives need to be provided in a typical aqueous coolant. Sudden provision of such large amounts of additives can cause a “slug” of material to precipitate and circulate in the system, which can result in damage and failure of pump seals. Accordingly, Hudgens et al U.S. Pat. No. 5,662,799 propose an elaborate diesel engine coolant filter that filters the coolant and releases an amount of additive through a diffusion tube, or alternatively through a diffusion wafer, into the coolant. Alternative versions of this approach are proposed by Tregidgo et al U.S. Pat. No. 5,435,346 and Cheadle et al U.S. Pat. No. 4,782,891, which utilize the corrosive nature of the coolant to erode a separating means, such as a rod, in the coolant filter and release anti-corrosive material.
Glycol freezing point depressants, such as ethylene glycol and the like, at the concentrations used in internal combustion engine coolants is toxic to various microbes. In addition, such engines operate at temperatures at which most microbes are killed, even in an all water coolant that would allow microbial growth readily at room temperature. Thus, typically no microbiocides or biocides are used in the coolants of internal combustion engines.
However, other coolant compositions and other liquid compositions are susceptible to microbial growth in normal use applications.
It would be advantageous to provide relatively low cost, quickly installed apparatus and methods that release microbiocides into such other coolant compositions and other liquid compositions susceptible to microbial growth at sustained rates to allow such compositions to function effectively without becoming unduly contaminated or otherwise significantly detrimentally affected by unwanted microbial growth.